This is my first time using the Mendez Stillman protocol to isolate chromatin via fractionation (usually for ChIP, I just lyse and shear away...), so this may be a dumb questions. But looking through the Mendez protocol, it appears that they tell you to keep supernatant fraction S2 (the supernatant left after centrifuging at 20,000g for 5 mins), but don't do anything with it later on. I just want to know, why S2 is kept, and what I am supposed to do with it?